In recent years, with the rapid development of mobile devices industry, the demand of high power, high power gain and high power added efficiency devices is also growing. The integrated circuits using compound semiconductor heterojunction bipolar transistors (HBTs) have been widely used in the power amplifier of mobile devices for their high power, high power gain, and high linearity. Therefore, by improving the layout design of the compound semiconductor HBT circuit, the power gain and power added efficiency of the HBT can be enhanced, and the competitiveness of the product containing the HBT can be increased.
The output power gain of an HBT is related to the base-collector junction capacitance, and the capacitance is proportional to the base area. The larger the ratio of the emitter area to the base area (EA/BA) is, the smaller the base-collector junction capacitance is. Therefore, by increasing the ratio of the emitter area to the base area, the base-collector junction capacitance can be effectively decreased, thereby enhancing the output power gain.